Introduction to Oracle REF Data Type

Oracle REF data type is a user-defined reference data type. This data type allows a column of one table to reference another table.

Syntax

The syntax for REF data type is as follows:

REF(type_name)

where type_name specifies the name of the reference type.

Use Cases

REF data type is commonly used in scenarios where relationships need to be established between different tables, such as managing and maintaining data relationships.

Examples

Example 1

Assume there is a table employees that contains information about employees, including employee_id, first_name, and last_name fields. Now we need to create a new table departments that contains information about departments, including department_id, department_name, and manager fields. To establish a relationship between the manager field in the departments table and the employee_id field in the employees table, we can use the REF data type. The specific steps are as follows:

First, create the employees table and insert data:

CREATE TABLE employees (
  employee_id NUMBER(6) PRIMARY KEY,
  first_name VARCHAR2(20),
  last_name VARCHAR2(20)
);

INSERT INTO employees VALUES (1001, 'John', 'Smith');
INSERT INTO employees VALUES (1002, 'Jane', 'Doe');

Then, create the departments table and use the REF data type to establish the relationship with the employees table:

CREATE TABLE departments (
  department_id NUMBER(6) PRIMARY KEY,
  department_name VARCHAR2(50),
  manager REF employees
);

ALTER TABLE departments ADD CONSTRAINT dept_mgr_fk
  FOREIGN KEY (manager) REFERENCES employees;

Finally, insert data into the departments table:

INSERT INTO departments VALUES (10, 'Sales', (SELECT REF(e) FROM employees e WHERE e.employee_id = 1001));
INSERT INTO departments VALUES (20, 'Marketing', (SELECT REF(e) FROM employees e WHERE e.employee_id = 1002));

You can query the data in the departments table using the following statement:

SELECT d.department_id, d.department_name, DEREF(d.manager).first_name, DEREF(d.manager).last_name
FROM departments d;

The result will be:

DEPARTMENT_ID  DEPARTMENT_NAME  DEREF(D.MANAGER).FIRST_NAME  DEREF(D.MANAGER).LAST_NAME
-------------  ---------------  ---------------------------  -------------------------
           10  Sales            John                         Smith
           20  Marketing        Jane                         Doe

Example 2

REF data type can also be used when querying employee information.

We can create a REF type for the Employee_Type as follows:

CREATE TYPE Employee_Ref_Type AS REF Employee_Type;

Now we can use the Employee_Ref_Type type to create a table to store employee information. Here is the SQL statement to create the table:

CREATE TABLE Employee_Ref_Table
(
   ID NUMBER(10) PRIMARY KEY,
   Name VARCHAR2(50),
   Dept VARCHAR2(50),
   Manager REF Employee_Ref_Type
);

Now we can insert employee information into the table. Here is the SQL statement to insert data:

INSERT INTO Employee_Table VALUES
(1, 'John Doe', 'IT', NULL);

INSERT INTO Employee_Table VALUES
(2, 'Jane Smith', 'Sales', NULL);

INSERT INTO Employee_Table VALUES
(3, 'Bob Johnson', 'Marketing', NULL);

Now we need to associate the above employee information with a manager. Here are the SQL statements:

UPDATE Employee_Ref_Table SET Manager =
(SELECT REF(e) FROM Employee_Table e WHERE e.ID = 1)
WHERE ID = 2;

UPDATE Employee_Ref_Table SET Manager =
(SELECT REF(e) FROM Employee_Table e WHERE e.ID = 1)
WHERE ID = 3;

Now, we can query the Employee_Ref_Table table to retrieve employee information along with their manager information. Here is the SQL statement to query employee information:

SELECT e.ID, e.Name, e.Dept, DEREF(e.Manager).Name AS Manager_Name
FROM Employee_Ref_Table e;

The query result is as follows:

ID   Name          Dept      Manager_Name
---  ------------  --------- ------------
1    John Doe      IT        (null)
2    Jane Smith    Sales     John Doe
3    Bob Johnson   Marketing John Doe

This example demonstrates how to use the REF data type to associate two tables. By using REF data type, we can easily associate tables without using foreign keys.

Conclusion

In Oracle database, the REF data type is a very useful data type. REF data type can be used to create objects with reference types that can be shared among different tables and queries. REF data type can be used to reduce redundant data storage and improve query efficiency. Using REF data type allows for more flexible database operations and better organization of data.